Trying to replicate the threads on a jar for the company i work for. How to extend length of the wrap
You should create the thread within the same mesh as the rest, but if we keep it as a separate mesh:


Put your 3D cursor at the center of this object. Set the 3D cursor as the Pivot Point. Select a part of the mesh.





Duplicate the selection with a ShiftD then Enter. Make the duplication rotate around the Z axis and with the 3D cursor as center.





Delete the former thread extremity.





Join the parts with W > LoopTools > Bridge.





You've got your shape.